在使用KeyListener进行游戏时需要帮助

Question

I would like the user to be able when to choose to start the game by pressing enter. In the keyPressed method, I've set it up to the best of my knowledge. However when I run the program the characters are already moving across the screen and pressing enter only speeds them up. If anyone could let me know what is going wrong and point me in the right direction I would be so grateful! Thanks.

Code:

import java.applet.*;
import java.awt.*;
import java.awt.event.*;
import javax.swing.*;

public class ZombieAttackMain extends Applet implements Runnable, KeyListener,  ActionListener{

    private Image background;

    Player p;
    NormalZombie nz;
    FastZombie fz;
    TankyZombie tz;
    Cow c1;
    Cow c2;
    Cow c3;
    Cow c4;
    Bullet b;

    private Graphics bufferGraphics;
    private Image offScreen;

    public final static int POSITION_1_Y = 100;
    public final static int POSITION_2_Y = 255;
    public final static int POSITION_3_Y = 400;
    public final static int POSITION_4_Y = 550;

    private boolean running = true;

    public void init(){
        setSize(1100, 700);
        background = getImage(getCodeBase(), "Background.jpg");
        p.player = getImage(getCodeBase(), "Player.png");
        nz.normalZombie = getImage(getCodeBase(), "NormalZombie.png");
        fz.fastZombie = getImage(getCodeBase(), "FastZombie.png");
        tz.tankyZombie = getImage(getCodeBase(), "TankyZombie.png");
        c1.cow = getImage(getCodeBase(), "Cow.png");
        c2.cow = getImage(getCodeBase(), "Cow.png");
        c3.cow = getImage(getCodeBase(), "Cow.png");
        c4.cow = getImage(getCodeBase(), "Cow.png");
        b.bullet = getImage(getCodeBase(), "Bullet.png");
        addKeyListener(this);
    }

    public void start() {
        p = new Player();
        nz = new NormalZombie();
        fz = new FastZombie();
        tz = new TankyZombie();
        c1 = new Cow();
        c2 = new Cow();
        c3 = new Cow();
        c4 = new Cow();
        b = new Bullet();
        Thread thread = new Thread(this);
        thread.start();
    }

    public void run() {
        while(running){
            if(nz.getNormalZombieXPosition() <= b.getBulletXPosition() && nz.getNormalZombieYPosition() >= b.getBulletYPosition() - 85
                    && nz.getNormalZombieYPosition() <= b.getBulletYPosition() + 85){
                nz.setShowNormalZombie(false);
                nz.setNormalZombieXPosition(1200);
                b.setShowBullet(false);
                b.setBulletXPosition(1200);
            }
            if(fz.getFastZombieXPosition() <= b.getBulletXPosition() && fz.getFastZombieYPosition() >= b.getBulletYPosition() - 85
                    && fz.getFastZombieYPosition() <= b.getBulletYPosition() + 85){
                fz.setShowFastZombie(false);
                fz.setFastZombieXPosition(1200);
                b.setShowBullet(false);
                b.setBulletXPosition(-500);
            }
            if(tz.getTankyZombieHP() == 2 && tz.getTankyZombieXPosition() <= b.getBulletXPosition() && tz.getTankyZombieYPosition()
                    >= b.getBulletYPosition() - 85 && tz.getTankyZombieYPosition() <= b.getBulletYPosition() + 85){
                b.setBulletXPosition(-500);
                b.setShowBullet(false);
                tz.setTankyZombieHP(1);
            }
            if(tz.getTankyZombieHP() == 1 && tz.getTankyZombieXPosition() <= b.getBulletXPosition() && tz.getTankyZombieYPosition()
                    >= b.getBulletYPosition() - 85 && tz.getTankyZombieYPosition() <= b.getBulletYPosition() + 85){
                b.setShowBullet(false);
                b.setBulletXPosition(-500);
                tz.setShowTankyZombie(false);
                tz.setTankyZombieXPosition(1200);
            }

            if(nz.getNormalZombieXPosition() <= c1.getCowXPosition() + 190 && nz.getNormalZombieYPosition() == POSITION_1_Y){
                c1.setShowCow1(false);
            }
            if(fz.getFastZombieXPosition() <= c1.getCowXPosition() + 190 && fz.getFastZombieYPosition() == POSITION_1_Y){
                c1.setShowCow1(false);
            }
            if(tz.getTankyZombieXPosition() <= c1.getCowXPosition() + 190 && tz.getTankyZombieYPosition() == POSITION_1_Y){
                c1.setShowCow1(false);
            }
            if(nz.getNormalZombieXPosition() <= c2.getCowXPosition() + 190 && nz.getNormalZombieYPosition() == POSITION_2_Y){
                c2.setShowCow2(false);
            }
            if(fz.getFastZombieXPosition() <= c2.getCowXPosition() + 190 && fz.getFastZombieYPosition() == POSITION_2_Y){
                c2.setShowCow2(false);
            }
            if(tz.getTankyZombieXPosition() <= c2.getCowXPosition() + 190 && tz.getTankyZombieYPosition() == POSITION_2_Y){
                c2.setShowCow2(false);
            }           
        if(nz.getNormalZombieXPosition() <= c3.getCowXPosition() + 190 && nz.getNormalZombieYPosition() == POSITION_3_Y){
                c3.setShowCow3(false);
            }
            if(fz.getFastZombieXPosition() <= c3.getCowXPosition() + 190 && fz.getFastZombieYPosition() == POSITION_3_Y){
                c3.setShowCow3(false);
            }
            if(tz.getTankyZombieXPosition() <= c3.getCowXPosition() + 190 && tz.getTankyZombieYPosition() == POSITION_3_Y){
                c3.setShowCow3(false);
            }
            if(nz.getNormalZombieXPosition() <= c4.getCowXPosition() + 190 && nz.getNormalZombieYPosition() == POSITION_4_Y){
                c4.setShowCow4(false);
            }
            if(fz.getFastZombieXPosition() <= c4.getCowXPosition() + 190 && fz.getFastZombieYPosition() == POSITION_4_Y){
                c4.setShowCow4(false);
            }
            if(tz.getTankyZombieXPosition() <= c4.getCowXPosition() + 190 && tz.getTankyZombieYPosition() == POSITION_4_Y){
                c4.setShowCow4(false);
            }

            repaint();
            try {
                Thread.sleep(17);
            } catch (InterruptedException e) {
                e.printStackTrace();
            }
        }
    }

    public void paint(Graphics g){
        g.drawImage(background,0,0,null);
        p.paint(g);
        if(nz.getShowNormalZombie() == true){
            nz.paint(g);
            nz.setNormalZombieXPosition(nz.getNormalZombieXPosition() + nz.getNormalZombieDx());
        }
        if(fz.getShowFastZombie() == true){
            fz.paint(g);
            fz.setFastZombieXPosition(fz.getFastZombieXPosition() + fz.getFastZombieDx());
        }
        if(tz.getShowTankyZombie() == true){
            tz.paint(g);
            tz.setTankyZombieXPosition(tz.getTankyZombieXPosition() +     tz.getTankyZombieDx());
        }
        if(c1.getShowCow1() == true){
            c1.paint(g);
            c1.setCowYPosition(POSITION_1_Y);
        }
        if(c2.getShowCow2() == true){
            c2.paint(g);
            c2.setCowYPosition(POSITION_2_Y);
        }
        if(c3.getShowCow3() == true){
            c3.paint(g);
            c3.setCowYPosition(POSITION_3_Y);
        }
        if(c4.getShowCow4() == true){
            c4.paint(g);
            c4.setCowYPosition(POSITION_4_Y);
        }
        if(b.getShowBullet()){
            b.paint(g);
            b.setBulletXPosition(b.getBulletXPosition() + b.getBulletDX());
            if(b.getBulletXPosition() > 1100){
                b.setShowBullet(false);
            }
        }
    }

    public void keyPressed(KeyEvent e) {
        switch(e.getKeyCode()){
        case KeyEvent.VK_UP:
            p.moveUp(p);
            break;
        case KeyEvent.VK_DOWN:
            p.moveDown(p);
            break;
        case KeyEvent.VK_SPACE:
            b.spawnBullet();
            break;
        case KeyEvent.VK_ENTER:
            start();
            break;
        }
    }

    public void update(Graphics g){
        if(offScreen == null){
            offScreen = createImage(this.getWidth(), this.getHeight());
            bufferGraphics = offScreen.getGraphics();
        }
        bufferGraphics.setColor(getBackground());
        bufferGraphics.fillRect(0,0,this.getWidth(),this.getHeight());
        bufferGraphics.setColor(getForeground());
        paint(bufferGraphics);
        g.drawImage(offScreen,0,0,this);
    }

    public static int getPosition1Y() {
        return POSITION_1_Y;
    }

    public static int getPosition2Y() {
        return POSITION_2_Y;
    }

    public static int getPosition3Y() {
        return POSITION_3_Y;
    }

    public static int getPosition4Y() {
        return POSITION_4_Y;
    }

    public void stop() {
        running = false;
    }

    public void keyReleased(KeyEvent e) {
    }
    public void keyTyped(KeyEvent e) {
    }
    public void actionPerformed(ActionEvent arg0) {     
    }
}

Answer 1

However when I run the program the characters are already moving across the screen and pressing enter only speeds them up

The start() method is invoked by the applet when it is loaded, so your game Thread starts automatically.

pressing enter only speeds them up

You invoke the start method again, so now you have two game Threads running.

Create a method called startGame() for example. Move the code from start() into that method. Then invoke startGame() when the Enter key is pressed. You would also want your code to make sure the game is currently not running so you don't start the game twice.

Answer 2

Hmmm... I'm not 100% sure, but it may have to do with the variable "Running". Try setting that to false, and then upon the user hitting "enter" set it to true.